1. Field of the Invention
The present invention relates to a process for producing a powdery rubber. More particularly, it relates to a process for producing a powdery rubber from an anionic or nonionic rubber latex which comprises treating the anionic or nonionic rubber latex to separate it into two phases i.e. a rubber particle phase and a water phase and then, adding an emulsion of a synthetic resin to absorb particles of the synthetic resin on the rubber particles and dehydrating and drying the resulting powdery rubber.
2. Description of the Prior Arts
Heretofore, rubber has been separated from a rubber latex and the separated rubber is supplied in a form of relatively large block, bulk or chip. However, it has been required to cut the rubber into fine pieces for certain uses or in certain applications. For example, when a blocked synthetic rubber is molded, the blocked rubber is cut into pieces and weighed and kneaded by suitable kneading methods using a Banbury mixer or a roll mixing blender.
In these cases, if the rubber is supplied in the form of powder or pellets, the step of cutting into fine pieces can be eliminated and the rubber can be automatically supplied to a weighing machine or a processing machine. Moreover, in the processing operation when the rubber is in the form of powder, the blend with various chemicals or fillers can be easily carried out advantageously.
Recently, the uses of the rubber with various thermoplastic resins in blend forms have increased depending on the increase of applications of the rubber.
The synthetic resins are usually supplied in the form of powder or pellets whereby the rubbers used for these purposes are preferably in the form of powder because of the uniform distribution of the synthetic rubber.
When the rubber is in a form of powder, the rubber can be quantitively and continuously supplied to a uniaxial extruder or a biaxial extruder together with the synthetic resin, whereby a continuous processing operation can be attained. In spite of these demands, most of the rubbers have been supplied in the block or chip form.
The rubbers have high tackiness or elasticity even at room temperature whereby even though the rubber is pelletized, the pellets adhere to each other to form blocks during storage or transfer.
Various methods have been studied to obtain powdery rubber which does not adhere to form blocks.
As the conventional methods, the following methods have been employed. The rubber is pulverized by a grinder and the pulverized rubber in the form of the suspension in air is mixed with an aqueous dispersion of an antiblocking agent such as talc, calcium carbonate. Water is then separated to obtain the powdery rubber which is further coated with a dusting powder.
The rubber is quenched to lower than brittle point by treating it with liquid nitrogen etc., and the rubber is pulverized by the ejection of jet flow or the application of ultrasonic waves and then coated with an antiblocking agent to obtain powdery rubber.
The rubber is separated from the latex by addition of a salt, an aqueous dispersion of carbon black is added under stirring and the resulting rubber mixture is dried and pulverized.
However, in these conventional methods, high degree of heat is generated by the friction of rubber caused by the elasticity or tackiness of the rubber whereby the elimination of the heat and the uniform pulverization are disadvantageously not easy, Moreover, this process is not economical because of its high cost, the power for pulverizing the rubber is limited and a large amount of the inorganic material is disadvantageously incorporated into the powdery rubber,